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Introductory Chemistry , 3 rd Edition Nivaldo Tro

Introductory Chemistry , 3 rd Edition Nivaldo Tro. Chapter 13 Solutions. Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA. 2009, Prentice Hall. Tragedy in Cameroon. Lake Nyos Lake in Cameroon, West Africa. On August 22, 1986, 1,700 people and 3,000 cattle died.

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Introductory Chemistry , 3 rd Edition Nivaldo Tro

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  1. Introductory Chemistry, 3rd EditionNivaldo Tro Chapter 13 Solutions Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA 2009, Prentice Hall

  2. Tragedy in Cameroon • Lake Nyos • Lake in Cameroon, West Africa. • On August 22, 1986, 1,700 people and 3,000 cattle died. • Released carbon dioxide cloud. • CO2 seeps in from underground and dissolves in lake water to levels above normal saturation. • Though not toxic, CO2 is heavier than air—the people died from asphyxiation. Tro's Introductory Chemistry, Chapter 13

  3. Tragedy in Cameroon:A Possible Solution • Scientists have studied Lake Nyos and similar lakes in the region to try and keep such a tragedy from reoccurring. • Currently, they are trying to keep the CO2 levels in the lake water from reaching the very high supersaturation levels by venting CO2 from the lake bottom with pipes. Tro's Introductory Chemistry, Chapter 13

  4. Solutions • Homogeneous mixtures. • Composition may vary from one sample to another. • Appears to be one substance, though really contains multiple materials. • Most homogeneous materials we encounter are actually solutions. • E.g., air and lake water. Tro's Introductory Chemistry, Chapter 13

  5. Solutions, Continued • Solute is the dissolved substance. • Seems to “disappear.” • “Takes on the state” of the solvent. • Solvent is the substance solute dissolves in. • Does not appear to change state. • When both solute and solvent have the same state, the solvent is the component present in the highest percentage. • Solutions in which the solvent is water are called aqueous solutions. Tro's Introductory Chemistry, Chapter 13

  6. Brass

  7. Common Types of Solution Tro's Introductory Chemistry, Chapter 13

  8. Solubility • When one substance (solute) dissolves in another (solvent) it is said to be soluble. • Salt is soluble in water. • Bromine is soluble in methylene chloride. • When one substance does not dissolve in another it is said to be insoluble. • Oil is insoluble in water. • The solubility of one substance in another depends on two factors: nature’s tendency towards mixing and the types of intermolecular attractive forces. Tro's Introductory Chemistry, Chapter 13

  9. Will It Dissolve? • Chemist’s rule of thumb: Like dissolves like • A chemical will dissolve in a solvent if it has a similar structure to the solvent. • When the solvent and solute structures are similar, the solvent molecules will attract the solute particles at least as well as the solute particles to each other. Tro's Introductory Chemistry, Chapter 13

  10. Classifying Solvents

  11. Will It Dissolve in Water? • Ions are attracted to polar solvents. • Many ionic compounds dissolve in water. • Generally, if the ions total charges < 4. • Polar molecules are attracted to polar solvents. • Table sugar, ethyl alcohol, and glucose all dissolve well in water. • Have either multiple OH groups or little CH. • Nonpolar molecules are attracted to nonpolar solvents. • b-carotene (C40H56) is not water soluble; it dissolves in fatty (nonpolar) tissues. • Many molecules have both polar and nonpolar structures—whether they will dissolve in water depends on the kind, number, and location of polar and nonpolar structural features in the molecule.

  12. Salt Dissolving in Water Tro's Introductory Chemistry, Chapter 13

  13. Solvated Ions When materials dissolve, the solvent molecules surround the solvent particles due to the solvent’s attractions for the solute. This process is called solvation. Solvated ions are effectively isolated from each other. Tro's Introductory Chemistry, Chapter 13

  14. Practice—Decide if Each of the Following Will Be Significantly Soluble in Water. • potassium iodide, KI • octane, C8H18 • methanol, CH3OH • copper, Cu • cetyl alcohol, CH3(CH2)14CH2OH • iron(III) sulfide, Fe2S3 • potassium iodide, KI soluble. • octane, C8H18insoluble. • methanol, CH3OH soluble. • copper, Cu insoluble. • cetyl alcohol, CH3(CH2)14CH2OH insoluble. • iron(III) sulfide, Fe2S3insoluble. Tro's Introductory Chemistry, Chapter 13

  15. Solubility • There is usually a limit to the solubility of one substance in another. • Gases are alwayssoluble in each other. • Two liquids that are mutually soluble are said to be miscible. • Alcohol and water are miscible. • Oil and water are immiscible. • The maximum amount of solute that can be dissolved in a given amount of solvent is called solubility. Tro's Introductory Chemistry, Chapter 13

  16. Descriptions of Solubility • Saturated solutions have the maximum amount of solute that will dissolve in that solvent at that temperature. • Unsaturated solutions can dissolve more solute. • Supersaturated solutions are holding more solute than they should be able to at that temperature. • Unstable. Tro's Introductory Chemistry, Chapter 13

  17. Supersaturated Solution A supersaturated solution has more dissolved solute than the solvent can hold. When disturbed, all the solute above the saturation level comes out of solution. Tro's Introductory Chemistry, Chapter 13

  18. Adding Solute to various Solutions Unsaturated Saturated Supersaturated Tro's Introductory Chemistry, Chapter 13

  19. Electrolytes • Electrolytes are substances whose aqueous solution is a conductor of electricity. • In strong electrolytes, all the electrolyte molecules are dissociated into ions. • In nonelectrolytes, none of the molecules are dissociated into ions. • In weak electrolytes, a small percentage of the molecules are dissociated into ions. Tro's Introductory Chemistry, Chapter 13

  20. Solubility and Temperature • The solubility of the solute in the solvent depends on the temperature. • Higher temperature = Higher solubility of solid in liquid. • Lower temperature = Higher solubility of gas in liquid.

  21. Changing Temperature = Changing Solubility • When a solution is saturated, it is holding the maximum amount of solute it can at that temperature. • If the temperature is changed, the solubility of the solute changes. • If a solution contains 71.3 g of NH4Cl in 100 g of water at 90 C, it will be saturated. • If the temperature drops to 20 C, the saturation level of NH4Cl drops to 37.2 g. • Therefore, 24.1 g of NH4Cl will precipitate. Tro's Introductory Chemistry, Chapter 13

  22. Purifying Solids:Recrystallization • When a solid precipitates from a solution, crystals of the pure solid form by arranging the particles in a crystal lattice. • Formation of the crystal lattice tends to reject impurities. • To purify a solid, chemists often make a saturated solution of it at high temperature; when it cools, the precipitated solid will have much less impurity than before. Tro's Introductory Chemistry, Chapter 13

  23. Solubility of Gases:Effect of Temperature • Many gases dissolve in water. • However, most have very limited solubility. • The solubility of a gas in a liquid decreases as the temperature increases. • Bubbles seen when tap water is heated (before the water boils) are gases that are dissolved, coming out of the solution. • Opposite of solids. Tro's Introductory Chemistry, Chapter 13

  24. Solubility of Gases:Effect of Pressure • The solubility of a gas is directly proportional to its partial pressure. • Henry’s law. • The solubility of solid is not effected by pressure. • The solubility of a gas in a liquid increases as the pressure increases. Tro's Introductory Chemistry, Chapter 13

  25. Solubility and Pressure • The solubility of gases in water depends on the pressure of the gas. • Higher pressure = higher solubility. Tro's Introductory Chemistry, Chapter 13

  26. Solubility and Pressure, Continued When soda pop is sealed, the CO2 is under pressure. Opening the container lowers the pressure, which decreases the solubility of CO2 and causes bubbles to form. Tro's Introductory Chemistry, Chapter 13

  27. Solution Concentrations Tro's Introductory Chemistry, Chapter 13

  28. Describing Solutions • Solutions have variable composition. • To describe a solution, you need to describe both the components and their relative amounts. • Dilute solutions have low amounts of solute per amount of solution. • Concentrated solutions have high amounts of solute per amount of solution. Tro's Introductory Chemistry, Chapter 13

  29. Concentrations—Quantitative Descriptions of Solutions • A more precise method for describing a solution is to quantify the amount of solute in a given amount of solution. • Concentration = Amount of solute in a given amount of solution. • Occasionally amount of solvent. Tro's Introductory Chemistry, Chapter 13

  30. Mass Percent • Parts of solute in every 100 parts solution. • If a solution is 0.9% by mass, then there are 0.9 grams of solute in every 100 grams of solution. • Or 10 kg solute in every 100 kg solution. • Since masses are additive, the mass of the solution is the sum of the masses of solute and solvent. Tro's Introductory Chemistry, Chapter 13

  31. mL H2O g H2O g EtOH, g H2O g sol’n % Example 13.1—Calculate the Mass Percent of a Solution Containing 27.5 g of Ethanol in 175 mL H2O. Given: Find: 27.5 g ethanol, 175 mL H2O % by mass 27.5 g ethanol, 202.5 g solution % by mass Solution Map: Relationships: 1 mL H2O = 1.00 g Solve: Check: The answer seems reasonable as it is less than 100%. Tro's Introductory Chemistry, Chapter 13

  32. Practice—Calculate the Mass Percent of a Solution that Has 10.0 g of I2 Dissolved in 150.0 g of Ethanol. Tro's Introductory Chemistry, Chapter 13

  33. g EtOH, g H2O g sol’n % Practice—Calculate the Mass Percent of a Solution that Has 10.0 g of I2 Dissolved in 150.0 g of Ethanol, Continued Given: Find: 10.0 g I2, 150.0 g ethanol H2O % by mass 10.0 g I2, 160.0 g solution % by mass Solution Map: Relationships: Solve: Check: The answer seems reasonable as it is less than 100%.

  34. Using Concentrations asConversion Factors • Concentrations show the relationship between the amount of solute and the amount of solvent. • 12% by mass sugar (aq) means 12 g sugar  100 g solution. • The concentration can then be used to convert the amount of solute into the amount of solution or visa versa. Tro's Introductory Chemistry, Chapter 13

  35. g solute g sol’n mL sol’n Example 13.2—What Volume of 11.5% by Mass Soda Contains 85.2 g of Sucrose? Given: Find: 85.2 g sugar volume, mL Solution Map: Relationships: 100 g sol’n = 11.5 g sugar, 1 mL solution = 1.00 g Solve: Check: The unit is correct. The magnitude seems reasonable as the mass of sugar  10% the volume of solution. Tro's Introductory Chemistry, Chapter 13

  36. Practice—Milk Is 4.5% by Mass Lactose. Determine the Mass of Lactose in 175 g of Milk. Tro's Introductory Chemistry, Chapter 13

  37. g solution g Lactose Practice—Milk Is 4.5% by Mass Lactose. Determine the Mass of Lactose in 175 g of Milk, Continued. Given: 175 g milk  175 g solution Find: g lactose Equivalence: 4.5 g lactose  100 g solution Solution Map: Apply Solution Map: Check Answer: Units are correct. Number makes sense because lactose is a component of the mixture, therefore, its amount should be less.

  38. Preparing a Solution • Need to know amount of solution and concentration of solution. • Calculate the mass of solute needed. • Start with amount of solution. • Use concentration as a conversion factor. • 5% by mass Þ 5 g solute  100 g solution. • “Dissolve the grams of solute in enough solvent to total the total amount of solution.” Tro's Introductory Chemistry, Chapter 13

  39. g solution g glucose Example—How Would You Prepare 250.0 g of 5.00% by Mass Glucose Solution (Normal Glucose)? Given: 250.0 g solution Find: g glucose Equivalence: 5.00 g glucose  100 g solution Solution Map: Apply Solution Map: Answer: Dissolve 12.5 g of glucose in enough water to total 250.0 g.

  40. Practice—How Would You Prepare 450.0 g of 15.0% by Mass Aqueous Ethanol? Tro's Introductory Chemistry, Chapter 13

  41. Practice—How Would You Prepare 450.0 g of 15.0% by Mass Aqueous Ethanol?, Continued Given: 450.0 g solution Find: g ethanol (EtOH) Equivalence: 15.0 g EtOH  100 g solution Solution map: g solution g EtOH Apply solution map: Answer: Dissolve 67.5 g of ethanol in enough water to total 450.0 g. Tro's Introductory Chemistry, Chapter 13

  42. moles of solute liters of solution Molarity = Solution ConcentrationMolarity • Moles of solute per 1 liter of solution. • Used because it describes how many molecules of solute in each liter of solution. • If a sugar solution concentration is 2.0 M , 1 liter of solution contains 2.0 moles of sugar, 2 liters = 4.0 moles sugar, 0.5 liters = 1.0 mole sugar: Tro's Introductory Chemistry, Chapter 13

  43. Weigh out 1 mole (58.45 g) of NaCl and add it to a 1.00 L volumetric flask. Add water to dissolve the NaCl, then add water to the mark. Swirl to mix. Step 1 Step 2 Step 3 Preparing a 1.00 M NaCl Solution Tro's Introductory Chemistry, Chapter 13

  44. g NaCl mol NaCl M L solution Example 13.3—Calculate the Molarity of a Solution Made by Dissolving 15.5 g of NaCl in 1.50 L of Solution Given: Find: 15.5 g NaCl, 1.50 L solution M Solution Map: Relationships: M = mol/L, 1 mol NaCl = 58.44 g Solve: Check: The unit is correct, the magnitude is reasonable. Tro's Introductory Chemistry, Chapter 13

  45. Practice—What Is the Molarity of a Solution Containing 3.4 g of NH3 (MM 17.03) in 200.0 mL of Solution? Tro's Introductory Chemistry, Chapter 13

  46. g NH3 mol NH3 M mL sol’n L sol’n Practice—What Is the Molarity of a Solution Containing 3.4 g of NH3 (MM 17.03) in 200.0 mL of Solution?, Continued Given: Find: 3.4 g NH3, 200.0 mL solution M Solution Map: Relationships: M = mol/L, 1 mol NH3 = 17.03 g, 1 mL = 0.001 L Solve: Check: The unit is correct, the magnitude is reasonable. Tro's Introductory Chemistry, Chapter 13

  47. Using Concentrations asConversion Factors • Concentrations show the relationship between the amount of solute and the amount of solvent. • 0.12 M sugar (aq) means 0.12 mol sugar  1.0 L solution. • The concentration can then be used to convert the moles of solute into the liters of solution, or visa versa. • Since we normally measure the amount of solute in grams, we will need to convert between grams and moles. Tro's Introductory Chemistry, Chapter 13

  48. mol NaOH L solution Example 13.4—How Many Liters of a 0.114 M NaOH Solution Contains 1.24 mol of NaOH? Given: Find: 1.24 mol NaOH volume, L Solution Map: Relationships: 1.00 L solution = 0.114 mol NaOH Solve: Check: The unit is correct, the magnitude seems reasonable as the moles of NaOH > 10x the amount in 1 L. Tro's Introductory Chemistry, Chapter 13

  49. Practice—Determine the Mass of CaCl2 (MM = 110.98) in 1.75 L of 1.50 M Solution. Tro's Introductory Chemistry, Chapter 13

  50. Practice—Determine the Mass of CaCl2 (MM = 110.98) in 1.75 L of 1.50 M Solution, Continued. Given: 1.75 L solution Find: g CaCl2 Equivalence: 1.50 mol CaCl2  1 L solution; 110.98 g = 1 mol CaCl2 Solution Map: L solution mol CaCl2 g CaCl2 Apply Solution Map: Check Answer: Units are correct. Tro's Introductory Chemistry, Chapter 13

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